The present invention provides a protective overcoat for photographic elements. More particularly the present invention provides an overcoat which is permeable to processing solutions and when subsequently fused provides water resistance and scratch protection to photographic elements.
Silver halide photographic elements contain light sensitive silver halide in a hydrophilic emulsion. An image is formed in the element by exposing the silver halide to light, or to other actinic radiation, and developing the exposed silver halide to reduce it to elemental silver.
In color photographic elements a dye image is formed as a consequence of silver halide development by one of several different processes. The most common is to allow a by-product of silver halide development, oxidized silver halide developing agent, to react with a dye forming compound called a coupler. The silver and unreacted silver halide are then removed from the photographic element, leaving a dye image.
In either case, formation of the image commonly involves liquid processing with aqueous solutions that must penetrate the surface of the element to come into contact with silver halide and coupler. Gelatin has been used exclusively in a variety of silver halide photographic systems as the primary binder due to its many unique properties, one of which is the water-swellable property. This rapid swelling allows processing chemistry to proceed and images to be formed. However, due to this same property, photographic images, whether they are on film or paper, need to be handled with extreme care so as not to come in contact with any aqueous solutions that may damage the images. Thus, although gelatin, and similar natural or synthetic hydrophilic polymers, have proven to be the binders of choice for silver halide photographic elements to facilitate contact between the silver halide crystal and aqueous processing solutions, they are not as tough and mar-resistant as would be desired for something that is handled in the way that an imaged photographic element may be handled. Thus, the imaged element can be easily marked by fingerprints, it can be scratched or tom and it can swell or otherwise deform when it is contacted with liquids.
There have been attempts over the years to provide protective layers for gelatin based photographic systems that will protect the images from damages by water or aqueous solutions. U.S. Pat. No. 2,173,480 describes a method of applying a colloidal suspension to moist film as the last step of photographic processing before drying. A series of patents describes methods of solvent coating a protective layer on the image after photographic processing is completed and are described in U.S. Pat. Nos. 2,259,009; 2,331,746; 2,798,004; 3,113,867; 3,190,197; 3,415,670 and 3,733,293. The application of UV-polymerizable monomers and oligomers on processed image followed by radiation exposure to form crosslinked protective layer is described U.S. Pat. Nos. 4,092,173; 4,171,979; 4,333,998 and 4,426,431. One drawback for the solvent coating method and the radiation cure method is the health and environmental concern of those chemicals to the coating operator. U.S. Pat. Nos. 3,397,980; 3,697,277 and 4,999,266 describe methods of laminating polymeric sheet film on the processed image as the protective layer. U.S. Pat. No. 5,447,832 describes the use of a protective layer containing mixture of high and low Tg latices as the water-resistance layer to preserve the antistat property of the V2O5 layer through photographic processing. This protective layer is not applicable to the image formation layers since it will detrimentally inhibit the photographic processing. U.S. Pat. No. 2,706,686 describes the formation of a lacquer finish for photographic emulsions, with the aim of providing water- and fingerprint-resistance by coating the emulsion, prior to exposure, with a porous layer that has a high degree of water permeability to the processing solutions. After processing, the lacquer layer is fused and coalesced into a continuous, impervious coating. The porous layer is achieved by coating a mixture of a lacquer and a solid removable extender (ammonium carbonate), and removing the extender by sublimation or dissolution during processing. The overcoat as described is coated as a suspension in an organic solvent, and thus is not desirable for large-scale application. U.S. Pat. No. 3,443,946 provides a roughened (matte) scratch-protective layer, but not a water-impermeable one. U.S. Pat. No. 3,502,501 provides protection against mechanical damage only, the layer in question contains a majority of hydrophilic polymeric materials, and must be permeable to water in order to maintain processability. U.S. Pat. No. 5,179,147 likewise provides a layer that is not water-protective.
U.S. Patent 5,856,051 incorporated by reference herein, describes a protective overcoat comprising hydrophobic polymer particles that have a particular melting point range, and gelatin. After photoprocessing development to produce the image, the photographic element is thermally fused so that the hydrophobic polymer particles form a water-resistant protective overcoat. The element described in the xe2x80x98051 patent, however, suffers in that this protective overcoat is easily scratched. The present invention discloses a uniquely structured overcoat that allows the photographic processing solutions to diffuse through for image formation, and then provides water resistance and improved scratch resistance properties compared to the one described in the ""051 patent.
Commonly assigned, copending USSN 09/312,378 (docket 79332), by the same inventors, discloses an imaged photographic element having a protective overcoat thereon, which protective overcoat comprises a first coating of hydrophobic polymer particles having an average size of 0.01 to 1 microns, a melting temperature of from 55 to 200xc2x0 C. at a weight percent of 30 to 95, and gelatin at a weight percent of 5 to 70. A second coating of abrasion resistant particles having an average size of from 0.01 to 1 microns is applied to form a second layer over the first layer.
There remains a need for an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, allows for appropriate diffusion of photographic processing solutions, and does not require coating operation after exposure and processing.
The present invention is an imaged photographic element having a protective overcoat thereon. The protective overcoat is formed by providing a photographic element having at least one silver halide light-sensitive emulsion layer. A first coating of hydrophobic polymer particles having an average size of 0.01 to 1 microns, a melting temperature of from 55 to 200 xc2x0 C. at a weight percent of 30 to 95, and gelatin or other hydrophilic polymer at a weight percent of 5 to 70 is applied to form a first layer over the silver halide light-sensitive emulsion layer. A second coating of abrasion resistant particles having an average size of from 0.01 to 1 microns is applied to form a second layer over the first layer. The coatings are dried at temperatures not exceeding the melting point of the particles used in the first coating, or of the glass transition temperature of the abrasion resistant particles used in the second coating, whichever is the lowest. The photographic element can be developed to provide an imaged photographic element. The first and second layers are fused to form a protective overcoat.
The present invention describes an imaged photographic element having an overcoat that imparts both water resistance and abrasion resistance. The protective overcoat of this invention can be achieved in one of the following manners. An uppermost overcoat layer, composed of abrasion resistant particles and optionally water soluble binders and optionally a fusible wax component, is coated over a second uppermost layer, which is composed of fusible particles and gelatin as described in U.S. Pat. No. 5,856,051. This entire package can then be imaged, processed, and fused. Alternately a water resistant fusible overcoat, as described in U.S. Pat. No. 5,856,051, is coated on silver halide containing photographic products. This photographic product is imaged and processed to generate an image. The abrasion resistant overcoat layer, composed of a hard particle component and optionally water soluble binders and optionally a fusible wax component is coated over this package and dried. The entire package is then fused.
In any case, the water-resistant overcoat, after being applied, is dried at temperatures essentially not exceeding the melting point of the particles used in the coating. If both the water-resistant overcoat and the abrasion resistant overcoat are dried together, they are dried at temperatures essentially not exceeding the melting point of the particles used in the first coating, or of the glass transition temperature of the abrasion resistant particles used in the second coating, whichever is the lowest. Otherwise, the particles will coalesce and form a hydrophobic barrier to the water-based chemical processing solutions, thus slowing image developability speed, which would be unacceptable.
Thus, when coating the imaging element with the protective coatings, it is necessary to avoid heating the coatings to above or near the Tg or melting point (whichever is lowest) of the overcoat polymers, so that they do not prematurely coalesce, before imaging and photoprocessing to form the image. Thus, the polymer particles in the imaging element (prior to photoprocessing) should not be in the form of a binder, but rather should form a filler and should not coalesce, thereby allowing the necessary permeability of processing solutions during photoprocessing. Preferably, the drying temperature is at least 1xc2x0 C below the Tg of the abrasion resistant particles, more preferably at least 5xc2x0 C. below, most preferably at least 10xc2x0 C. below the Tg of the abrasion resistant particles. The particles are for the purpose of providing abrasion resistance and, hence, can be distinguished from other inorganic particles made from conductive materials, used for another purpose.
The structured overcoat of this invention is composed of hard abrasion resistant particles that are stratified in the overcoat layer and which, after fusing, provide the most effective resistance to scratches. The present invention provides scratch (abrasion) resistance to a photographic element that is water-resistant.
The present invention provides a first overcoat formulation to the emulsion side of photographic products, particularly photographic prints. The first overcoat formulation of the present invention includes 30-95% by weight (based on the dry laydown of the overcoat) of hydrophobic polymer particles having an average size of 0.01-1 microns, preferably 0.01 to 0.5 microns and 5-70% by weight (based on the dry laydown of the overcoat) of a hydrophilic polymer, preferably gelatin, as binder. Gelatin includes lime processed gelatin, acid processed gelatin and modified gelatin as described in U.S Pat. Nos. 5,219,992 and 5,316,902. Other common addenda, such as hardeners, spreading agents, charge control agents, surfactants and lubricants can also be included in the formulation as needed. The hydrophobic polymer of this invention has melting temperature (Tm) of 55-200xc2x0 C., and forms a water-resistant layer by fusing the polymer particles at a temperature above the Tm after the sample has been processed to generate the image. Since the particle size of the polymer is small, the overcoat layer will not adversely affect the sharpness of the image due to light scattering, as observed for other large particle fillers. The presence of 5-70% by weight of gelatin is sufficient to allow proper permeability for processing solution to diffuse in and out for image development and also retain particles in the layer during processing. The coating solution is aqueous and can be incorporated in the manufacturing coating operation without any equipment modification. The fusing step is simple and environmentally friendly to photofinishing laboratories. Polymer of choice can be any hydrophobic polymer or copolymer as long as the melting temperature is above 55xc2x0 C. and below 200xc2x0 C. The lower limit is to prevent premature coalescence from occurring prior to photographic processing, and the upper limit is to prevent destruction of the paper support and imaging chemicals during fusing. These types of hydrophobic particles (polymers) include dispersions of submicron size, from 0.01 xcexcm to 1 xcexcm wax particles such as those offered commercially as aqueous or non-aqueous dispersions of polyolefins, polypropylene, polyethylene, high density polyethylene, oxidized polyethylene, ethylene acrylic acid copolymers, microcrystalline wax, paraffin, and natural waxes such as carnauba wax, and aqueous dispersions of synthetic waxes from such companies as, but not limited to, Chemical Corporation of America (Chemcor), Inc., Michelman Inc., Shamrock Technologies Inc., Daniel Products Company. The dispersion may also contain dispersing aids such as polyethylene glycol.
Instead of gelatin or in addition to gelatin, other hydrophilic polymers, including water-soluble polymers, can be used, especially if they can improve the developability and dye formation rate of the imaging formation layer, especially noticeable for the layers closer to the support. During processing, the water soluble polymers can be removed from the coating, typically in amounts of at least 25% by weight of the water-soluble polymers, and therefore do not interfere with the formation of water resistance layer by fusing treatment. The average molecular weight of the water-soluble polymers is between 1,000 and 200,000, preferably between 1,500 and 20,000. A wide variety of nonionic, anionic or cationic water soluble polymers can be used in the present invention including polyacrylamides, polymethacrylamide, poly(acrylic acid), poly(methacrylic acid), poly(ethylene oxide), poly(oxymethylene), poly(vinyl alcohol), polyvinylamine, polyvinylpyrrolidone, poly(ethyl oxazoline), poly(vinyl pyridine), poly(ethylene imine), poly(ethylene glycol methacrylate), poly(hydroxyethyl methacrylate), poly(vinyl methyl ether), methyl cellulose, hydroxy propyl cellulose, hydroxy ethyl cellulose, hydroxy propyl methyl cellulose, poly(styrene sulfonic acid), poly(ethylene sulfonic acid), poly(vinyl phosphoric acid), poly(maleic acid), or copolymers containing sufficient amount of hydrophilic functional groups to be water soluble, and combinations thereof.
The second layer of the overcoat is composed of hard abrasion resistant particles, either a sub-micron size inorganic oxide particle such as silicon oxide, aluminum oxide, titanium oxide, or a polymer or copolymer particle that is comprised of a significant amount ( greater than 40%) of a monomer precursor to a polymer having modulus that is higher than that of polyethylene and thus provides good abrasion resistance. Moduli listings for polyethylene and many polymers can be found in general plastics references such as Modern Plastics Encyclopedia, October Volume 67, number 11 (1990). Such polymers include, for example polyacrylates and polymethacrylates such as polymethyl methacrylate, polyphenylmethacrylate, polyethylmethacrylate, polymethylacrylate, and copolymers with acrylic or methacrylic acid or minor amounts of other polymeric components, cellulose esters such as cellulose diacetates and triacetates, cellulose acetate butyrate, cellulose nitrate, or sulfonates, polyesters, polyurethanes, urea resins, melamine resins, urea-formaldehyde resins, polyacetals, polybutyrals, polyvinyl alcohol, epoxies and epoxy acrylates, phenoxy resins, polycarbonates, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl-alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid polymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, vinylidine chloride-acrylonitrile - acrylic acid copolymers, acrylic ester-acrylonitrile copolymers, acrylic ester-vinylidene chloride copolymers, methacrylic ester-styrene copolymers, butadiene-acrylonitrile copolymers, acrylonitrile-butadiene-acrylic or methacrylic acid copolymers. Polyacrylates and polymethacrylates such as polymethyl methacrylate, polyphenylmethacrylate, polyethylmethacrylate, polymethylacrylate, and copolymers with acrylic or methacrylic acid are preferred.
These hard abrasion resistant particle components can optionally contain minor amounts of hydrophilic components, such as, itaconic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid-sodium salt, 2-hydroxyethyl acrylate, 2-methacryloyloxyethyl-1-sulfonic acid-sodium salt and others commonly known in the art.
These hard abrasion resistant particle components can optionally contain minor amounts of crosslinking agents such as divinyl benzene, 1,4-butyleneglycol methacrylate, trimethylpropane triacrylate, ethyleneglycol dimethacrylate and others commonly known in the art.
Other common addenda, such as hardeners, spreading agents,charge control agents, surfactants and lubricants can also be included in the formulation as needed.
The imaged photographic elements protected in accordance with this invention are derived from silver halide photographic elements that can be black and white elements (for example, those which yield a silver image or those which yield a neutral tone image from a mixture of dye forming couplers), single color elements or multicolor elements. Multicolor elements typically contain dye image-forming units sensitive to each of the three primary regions of the spectrum. The imaged elements can be imaged elements which are viewed by transmission, such a negative film images, reversal film images and motion picture prints or they can be imaged elements that are viewed by reflection, such as paper prints. Because of the amount of handling that can occur with paper prints and motion picture prints, they are preferred imaged photographic elements for use in this invention.
The photographic elements in which the images to be protected are formed can have the structures and components shown in Research Disclosure 37038. Specific photographic elements can be those shown on pages 96-98 of Research Disclosure 37038 as Color Paper Elements 1 and 2. A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. All of these can be coated on a support which can be transparent (for example, a film support) or reflective (for example, a paper support). Support bases that can be used include both transparent bases, such as those prepared from polyethylene terephthalate, polyethylene naphthalate, cellulosics, such as cellulose acetate, cellulose diacetate, cellulose triacetate, glass, and reflective bases such as paper, coated papers, melt-extrusion-coated paper, and laminated papers, such as biaxally oriented support laminates. Biaxally oriented support laminates are described in U.S. Pat. U.S. No. 5,853,965; U.S. Pat. No. 5,866,282; U.S. Pat. No. 5,874,205; U.S. Pat. No. 5,888,643; U.S. Pat. No. 5,888,681; U.S. Pat. No. 5,888,683; and U.S. Pat. No. 5,888,714 incorporated by reference herein. These biaxally oriented supports include a paper base and a biaxially oriented polyolefin sheet, typically polypropylene, laminated to one or both sides of the paper base. At least one photosensitive silver halide layer is applied to the biaxially oriented polyolefin sheet. Photographic elements protected in accordance with the present invention may also include a magnetic recording material as described in Research Disclosure, Item 34390, November 1992, or a transparent magnetic recording layer such as a layer containing magnetic particles on the underside of a transparent support as described in U.S. Pat. No. 4,279,945 and U.S. Pat. No. 4,302,523.
Suitable silver halide emulsions and their preparation, as well as methods of chemical and spectral sensitization, are described in Sections I through V of Research Disclosure 37038. Color materials and development modifiers are described in Sections V through XX of Research Disclosure 37038. Vehicles are described in Section II of Research Disclosure 37038, and various additives such as brighteners, antifoggants, stabilizers, light absorbing and scattering materials, hardeners, coating aids, plasticizers, lubricants and matting agents are described in Sections VI through X and XI through XIV of Research Disclosure 37038. Processing methods and agents are described in Sections XIX and XX Research Disclosure 37038, and methods of exposure are described in Section XVI of Research Disclosure 37038.
Photographic elements typically provide the silver halide in the form of an emulsion. Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like). Also useful as vehicles or vehicle extenders are hydrophilic water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like.
Photographic elements can be imagewise exposed using a variety of techniques. Typically exposure is to light in the visible region of the spectrum, and typically is of a live image through a lens. Exposure can also be to a stored image (such as a computer stored image) by means of light emitting devices (such as LEDs, lasers, CRTs, etc.).
Images can be developed in photographic elements in any of a number of well known photographic processes utilizing any of a number of well known processing compositions, described, for example, in T. H. James, editor, The Theory of the Photographic Process, 4th Edition, Macmillan, New York, 1977. In the case of processing a color negative element, the element is treated with a color developer (that is one which will form the colored image dyes with the color couplers), and then with an oxidizer and a solvent to remove silver and silver halide. In the case of processing a color reversal element or color paper element, the element is first treated with a black and white developer (that is, a developer which does not form colored dyes with the coupler compounds) followed by a treatment to render developable unexposed silver halide (usually chemical or light fogging), followed by treatment with a color developer. Development is followed by bleach-fixing, to remove silver or silver halide, washing and drying.